1. Field of the Invention
This invention relates to a hue identifying apparatus for use in color printing, and more particularly to an apparatus for determining whether a predetermined hue is contained in a color photographic film.
2. Description of the Prior Art
Among the objects which are commonly recorded on color photographic film, many have hues which are well known. These include, for example, the faces of people, the blue sky, lawns, snow and the like. The fact that these hues are well known makes the work of finishing them particularly interesting. Therefore, it has been proposed to define the hue of a given object in advance, investigate whether the defined hue is contained in each section of the image area, and print the image so as to satisfactorily finish the defined hue when the quantity of the hue contained in the image area is more than the predetermined value.
In this printing method, a hue extracting system is used to determine the existence of the predetermined hue in the image area. The hue extracting system consists of a scanner for scanning each section of the image area, a measuring device for measuring the transmitted light at each scanning spot to obtain blue, green and red density values, an operation means for compensating for differences in the characteristics of photosensitive materials and determining normalized densities of the three colors corresponding to the exposure of the object, and a hue identifying apparatus for determining on the basis of the normalized three-color densities whether the hue of the object is identical with the predetermined one.
In a conventional hue identifying apparatus, for example as described in Japanese unexamined Patent Publication No. 53(1978)-145621, a predetermined region is defined by a polygon drawn on an orthogonal coordinate system, with a combination of two color densities of the three as a coordinate axis and another combination of two color densities as the other axis, and a plurality of equations are used to determine whether the hue at each point of the image area is included in the predetermined region. With the conventional apparatus, however, a comparator is used to conduct the calculation of the equations. Therefore, when the shape of the hue region is complicated, it becomes necessary to use many comparators and the construction of the apparatus becomes complicated.
Further, with the above-described conventional apparatus, different sets of equations must be used for different hue regions. This necessitates a change in the reference voltage of the comparator, so that troublesome adjustments are required.
Furthermore, when a plurality of hues are to be detected, it is necessary to construct circuits for the respective hues, making it necessary to provide a complicated and expensive apparatus.
In addition, in case the hue region is defined in terms of an orthogonal coordinate system, the linearity of the characteristic curve of the color photographic film cannot be maintained at the under-exposure and over-exposure sections. Particularly, at the extreme under-exposure and extreme over-exposure sections, the image information disappears, and data corresponding to the hue of the object cannot be obtained by normalization based on gamma compensation and sensitivity compensation. Particularly at the extreme under-exposure section, the hue deviates greatly with fluctuation of the mask density and very small differences in the normalizing conditions.